The study of the natural history of periodontal disease in Sri Lankan tea laborers is continuing. Three sub-populations have been identified, based on rates of periodontal disease destruction and tooth loss due to periodontal disease: (1) approximately 10% of the group had rapid progression (RP) and extensive tooth mortality; (2) approximately 10% showed no progression (NP) of the disease and (3) approximately 80% showed moderate progression (MP) of periodontal destruction. Bacteriological, immunological, radiographic and genetic studies of the three populations are under way. The specific aims of these studies are to compare the presence and levels of selected putative periodontal pathogens, peripheral blood antibody titers and to evaluate the genetic determinants in the three groups. Building of two master data sets in SAS for the longitudinal Norwegian surveys 1968-1985 (15) was completed. Data bases are: LOE.NOR.AVO (all valid observations) and LOE.NOR.IAS (in all surveys). Continued studies have focused on the stability of the gingival lesion, the mean number of years needed for an inflamed gingival unit to convert to progressive loss of attachment and the factors which may influence the continuity and discontinuity of the destruction of the periodontium.